The reasoning behind base layers, and when to use them. If your into other outdoor sports, sports like mountaineering or skiing you will already have some concept of layering especially for winter.
Multiple layers help trap air which warms up and keeps you warmer, specific layers can also help the transfer of sweat from the skin to an outer garment keeping you drier -- and dry is warmer than wet ,this all makes sense.
What most people don't understand or even consider is the role of base layers during mild and hot weather.
Not all base layers are the same some are designed to actively cool you -- some are designed to passively regulate temperature, some are designed to move moisture some are designed for warmth, you need a very different base layer for 35c than 2c.
There are 3 main reasons for wearing a base layer these are as applicable/more applicable in summer as in winter they all aid comfort but the specifics are.
1. Moisture management either through capillary action or chemical treatments - a base layer sucks or absorbs moisture (in the form of sweat) away from the skin where it can evaporate. Imagine if you will climbing a hill in direct sunlight without a base layer, at the top you are sweating your cycling jersey is soaked and then you plunge instantly down the shaded northern flanks of the hill -- that hot sweat turns into a cold wet compress. Our best moisture management base layer is the Castelli Pro Issue it uses capillary action to move sweat away it also has a 3D knit meaning it can trap air for;
2. Temperature management By having air pockets in a base layer the skin stays drier and more comfortable at your body better regulates its temperature -- old fashioned style string vests but in modern fabrics are best at temperature regulation. Check out the Castelli Core Mesh base layer for the perfect next to skin experience keeping your body nice and dry all year round.
3. Protection Base layers can provide protection in multiple ways the first is in the form of slip slide
Slip Slide, if you crash with just a jersey on you will get friction burns and possibly even melted polyester jersey sticking to your skin -- using a base layer allows a lot of the friction to be dissipated meaning your less likely to get superficial injuries. There are some people that claim a base layer can even help reduce the chances of a broken collarbone. (Personally I think this is more circumstantial evidence -- experienced riders tend to wear a base layer -- experienced riders know to roll in a crash if possible. Inexperienced riders tend to not wear base layers inexperienced riders tend to stick their arms out in a crash). But certainly you will always be better off crashing with a base layer than without., but lets all try and not crash please.
UV Protection, it's a glorious hot sunny day you wear your open mesh cycling jersey to keep you "cool" and bam what happens? You get burnt through your jersey , not only are the long term health risks of sunburn pretty dire reading, if your on a long ride and you get burnt you get hot - you get dehydrated - you go slower which means you have more exposure -- so you dehydrate more - you get hotter -- there is a pattern here... The Castelli Active Cooling Base layer has 50+UPF protection keeping you sun burn free if your riding in intense sunlight or you are susceptible to the suns harmful rays don't just rely on a jersey
Heat Stroke The Castelli Active Cooling Base layer also has active cooling (and a pretty swanky dynamic print that shows if its working) so by wearing this base layer not only do you keep the suns harmful rays off your body it actually cools you more efficiently than your body can manage on its own making you perform at your optimum.
Protection from wind. Castelli even offer base layers with windstopper panels (we have a new one coming and its secret for now ssshhhh) so if your in an early season race and your team don't supply you with a team gilet you can wear this under your jersey to have the looks and the protection.
Protection from cold -- this is the one most people think about and really it's a combination of trapped air and moisture management but with a semi solid state these base layers are often called thermals a they offer thermal protection our warmest base layer is the aptly named Flanders Warm ( we also have a zip collar version Flanders Warm Zip -- who thought up these innovative names)
Protecting your modesty - some cycling jerseys are very see through to some people men and women can find this a little disconcerting, a base layer under a jersey will as we have seen make you more comfortable on the bike -- it will also allow you to be more comfortable in the café mid ride. This is possibly a good time to also mention the Rosso Corsa Light Bra this Bra works like our base layers offering maximum ventilation and moisture management as well as modesty with a cycling specific tuned support.
If your still not convinced there is another very good reason for wearing a base layer on cool wet or windy days. Most technical jackets and mid to outer layers rely on a dedicated base layer to allow them to work -- something like the Gabba or the Tempesta rain jacket worn next to the skin cant do its job. When your body sweats, its creating actual liquid moisture this will condenses on the inside of the garment and cant go anywhere. Breathable garments rely on the fact moisture vapour is smaller than a moisture droplets ,a base layer helps regulate your sweat keeping it in vapour form to allow your very expensive " breathable" jacket or jersey to work your base layer also absorbs the salts and minerals you sweat out stopping them from blocking the pores in your breathable jacket or jersey.
It is worth noting that Castelli do offer some jerseys that are designed to be worn next to the skin the Climbers 2 for instance so this ultra light jersey wicks and breaths and dries almost instantly like our base layers (just remember to use sunscreen). However for the majority of the year (especially in the UK) and with the vast majority of outer wear a base layer will enhance your comfort levels and your performance and in the event of an accident it will also offer a little bit of skin protection.